Description: Shorter proof of nfs1 (three essential steps instead of four). (Contributed by BJ, 2-May-2019) (Proof modification is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Hypothesis | bj-nfs1.nf | |- F/ y ph |
|
| Assertion | bj-nfs1 | |- F/ x [ y / x ] ph |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | bj-nfs1.nf | |- F/ y ph |
|
| 2 | bj-nfs1t2 | |- ( A. x F/ y ph -> F/ x [ y / x ] ph ) |
|
| 3 | 2 1 | mpg | |- F/ x [ y / x ] ph |